ByGEORGE B. MERRYMarch 1, 1984

Political campaigns are becoming so drawn out that many voters are turned off long before balloting time. Yet many of those who should be most concerned - the candidates themselves - exhibit little interest in shortening the process.

This is particularly apparent in Massachusetts, where Democrats have been scrambling to succeed retiring US Sen. Paul E. Tsongas. It's more than six months until next September's party primary, but there's no doubt the candidates would have been off and running even earlier if Senator Tsongas had reached his decision sooner.

One reason is a controversial party rule: Those who want to compete for the senatorial nomination in the state primary first must win at least 15 percent of the delegate votes in the party's pre-primary convention June 9.

But most of the 4,300 delegates who will attend on June 9 were chosen Feb. 11 at town and ward Democratic caucuses. Because of this early date, would-be Tsongas successors were under the political gun to get cracking very early in the game.

State Democratic leaders could have deferred the delegate-selection process until late April or even early May. That would have shortened the campaign season, and contenders for the Senate seat would have more time to launch their efforts before making their intentions public. Such a delay also might have narrowed the field of candidates, reduced the amount of spending, and focused the campaign more sharply.

The seven contenders for the Tsongas chair are David M. Bartley, president of Holyoke Community College; Michael Joseph Connolly, Massachusetts secretary of state; William H. Hebert, former president of the Massachusetts Teachers Association (MTA); John F. Kerry, lieutenant governor; John Pierce Lynch, former register of deeds in Hampden County; and Edward J. Markey and James M. Shannon, US representatives.

Most of the Democratic hopefuls currently hold elective office or have professional responsibilities. And they started their campaigns in January or February for a position that won't be open until early next year, taking valuable time away from what they now are doing, or supposed to be doing.

By making their move so early, candidates invite voter boredom. Between now and primary day, the challenge for Democratic senatorial candidates will be to keep from becoming shopworn from too much campaigning.

Even if the Democratic state convention endorses no candidate on the first ballot, it's unlikely all seven senatorial aspirants will win the necessary 15 percent backing.

Mr. Lynch may be hard hit by the party rule. Despite his 30 years as a county official, he may not be well known within party ranks outside of western Massachusetts.

Dr. Hebert, too, is a political newcomer, although he is known within teacher union ranks. And a substantial number of delegates chosen to the June 9 convention in Worcester are MTA members, which could boost his prospects for making it onto the Democratic primary ballot in September.

Mr. Bartley is also counting on support from within teacher circles. He is probably well-known across the commonwealth, particularly among political activists, because he served seven years as speaker of the state House of Representatives and later returned to Beacon Hill as secretary of administration and finance under former Gov. Edward J. King. This, coupled with the fact that he is from western Massachusetts, could be an asset. Except for Lynch, all other aspirants live within or just outside of Route 128.

Mr. Connolly has been trying to separate himself from other liberal-leaning candidates by opposing federal funding of abortions (which they support). And the fact that he is the only Bostonian in the pack could help him.

Mr. Kerry, a former assistant district attorney in Middlesex County, intends to capitalize on his expertise in the criminal-justice field and his experience in Washington as the state administration's liaison in federal relations.

Aiding Congressman Markey's candidacy may be his well-publicized support of the nuclear-freeze movement and activist role on the environmental front.

Congressman Shannon, who has won the endorsement of US Speaker Thomas P. O'Neill Jr. (D) of Massachusetts, has been close to Tsongas. When Tsongas was elected to the Senate six years ago, Shannon succeeded him in the Fifth District seat.

However, Shannon cannot expect Tsongas' backing unless and until he wins the Democratic senatorial nomination. Tsongas has pledged not to take sides in the battle for the Senate nomination.

Gov. Michael S. Dukakis, too, has declined to involve himself in anyone's campaign. This must be a disappointment to Kerry, who serves with the governor on Beacon Hill.

Like it or not, Bay State voters will be seeing much of and hearing a lot from the candidates. The seven squared off Feb. 18 in the first of what could be a lengthy, even tiresome, parade of debates.